The thruster is particularly intended for installing on the bow and/or the stern of a boat. The function of such thrusters is to provide thrust that is lateral or longitudinal depending on the disposition of the propeller axis relative to the longitudinal direction of the vessel. They enable propulsion to be applied in both directions, thereby enabling a vessel to move omnidirectionally, particularly while maneuvering, and while correcting drift due to wind and current or to residual way.
More particularly, the present invention relates to a retractable thruster for a surface or submersible vessel, the thruster comprising a propulsion assembly comprising a rigid structure containing or suitable for containing a motor driving in rotation at least one propeller placed inside a turbine, via at least one rotary shaft between said motor and said propeller, and preferably a hull closure plate placed beneath said turbine and secured thereto, said propulsion assembly being movable by displacement means between a rest, position A retracted inside the hull, and a deployed position B for propulsion, in which the propeller is immersed beneath the hull.
The propeller axis is generally perpendicular to the axis of the motor, and the motor co-operates with the propeller via a geared angle take-off device comprising a first rotary shaft extending a motor shaft situated on the axis of the motor, said first rotary shaft rotating a second shaft perpendicular to said first rotary shaft and having the propeller mounted thereon.
The angle take-off device, also referred to as a “shoulder”, is thus essentially contained in the turbine.
In known manner, the angle take-off device comprises a casing containing two shafts rotating respectively about two perpendicular axes of rotation, and comprising both a first shaft rotated directly or indirectly by said motor and a second shaft driving at least one propeller in rotation, together with mechanical elements such as gearing made up of gearwheels, ball bearings, or smooth bearings, thereby enabling rotation to be transmitted from said first shaft to said second shaft.
Casings of the above type are described in French patent No. 2 798 184 in the name of the Applicant.
The first rotary shaft rotated at its top end by a motor can co-operate in the angle take-off device with one or two perpendicular shafts each rotating a propeller having an axis of rotation extending in the same direction perpendicular to said first rotary shaft(s). When the thruster is provided with two propellers in known manner, the first propeller is a traction propeller boosting the second propeller which is a propulsion propeller, and vice versa by reversing the direction of rotation, providing an assembly that is very effective and that provides thrust symmetrically in both directions.
Retractable thrusters are described in the following patents: FR 2 652 559, FR 2 741 854, and EP 0 863 837.
A retractable thruster includes a device for retracting and extending the propeller relative to the hull.
In EP 0 863 837, a displacement device is described delivering rectilinear up and down movement to the propulsion assembly, enabling the propeller to be retracted into a well within the hull or to be extended beneath the hull. A transverse “antitorque” or “antirotation” plate secured to the thruster is situated inside the well and is of shape complementary to the well so as to prevent the thruster from turning relative to the boat while delivering thrust, where such turning can be the result of a torque effect, hence the term “antitorque plate”. The device described in EP 0 863 837 also includes means for preventing the thruster becoming jammed or wedged in its rectilinear up and down movements.
The devices for moving the propulsion assembly as described in EP 0 863 837 present a major drawback, namely the rectilinear displacement of the propulsion assembly within the hull occupies a large volume therein.
In FR 2 652 559, proposals are made for a deformably rotatable trapezoidal device generating rectilinear extension or retraction movement of the propulsion assembly out from or into a well that enables the total volume needed for the thruster to be reduced, particularly in the height direction. Nevertheless, that trapezoidal device with its asymmetrically pivoting arms co-operating with a bracket secured to the turbine enables the propeller axis to be moved in rectilinear manner while the propeller is being extended from or retracted into the well, thus enabling the propeller to be cleared immediately by putting the mechanism into action.
The device for retracting and extending the thruster as described in FR 2 652 559 reduces the space occupied by the thruster, particularly in a vertical direction, since the thruster can be disposed in inclined manner inside the hull and can be deployed outside the hull while remaining inclined.
Devices are also known for retracting and extending the propulsion assembly in which the propeller is cleared not by imparting vertical rectilinear movement to the propeller axis, but by imparting circular movement by pivoting the propulsion assembly about a stationary pivot shaft situated at some height inside the hull. In that device, the propulsion assembly is like a swinging arm with the propeller at its end being moved through a circular movement relative to the pivot shaft at the opposite end of said arm.
It is necessary to extend part of the “arm” outside the hull in order to enable the propeller to be fully extended, thus requiring an opening in the hull that is greater than that needed merely for passing the turbine. That large opening involves large volumes and weight of water being displaced or contained that are excessive and that endanger the mechanical reliability of the propulsion system as a whole, while also increasing the weight at the bow end of the vessel in disadvantageous manner.